It is known in the art that surface plasmon resonance in nano scale structures, such as nanoparticles, can be used for directing electromagnetic radiation in the visible spectrum in a manner similar to the directional transmission by radiofrequency antennas. For example, in the radiofrequency spectrum, a typical antenna design for high directivity is the Yagi-Uda antenna, which comprises a linear array of antenna elements, where an array of nanoparticles can provide a similar radiation pattern in the optical regime. Directional control of visible spectrum radiation can thus be obtained by a nano-optical Yagi-Uda antenna comprising, for example, an appropriately configured arrangement of gold nano rods.
Plasmonic antennas may be useful components for microscopic or nano scale optical systems. For example, sending or receiving photons in a directionally selective fashion may find application in the field of micro- and nano scale photonics. By such directional sending or receiving of photons, signals may be transmitted in a well-defined direction or the signal to noise ratio of a detector may be increased by such directionally selective components. Furthermore, wavelength dependent directivity may be particularly advantageous for scaling sensors. Plasmonic sensors are usually based on detecting changes in the spectrum of radiation coming from an object of interest, e.g. scattered, transmitted or fluorescent radiation. Spectral information is typically recovered by gratings or filters. These components are large compared to plasmonic antennas, and furthermore are hard to miniaturize. If the spectral information would already be present in the scatter or emission patterns coming from the antenna this can simplify spectral analysis, and thus may result in cheaper, more compact devices.
The split ring resonator has been studied in the art as an artificial magnetic atom. It has also been shown, for example by Yao Jie et al. in “An Antenna to Direct Radiation to Opposite Directions,” Optics Communications 300, p. 274-276, that a split ring resonator can be used as an optical antenna to direct radiation emitted by an electric source to different directions at different wavelengths. This phenomenon, according to Jie et al., can be explained by a two-dipole model.